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Pellet-Size Estimation of a Ferrochrome Pelletizer Circuit Using Computer Vision Techniques

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Pellet-Size Estimation of a Ferrochrome Pelletizer Circuit Using Computer Vision Techniques Pellet-size estimation of a ferrochrome pelletizer circuit using Computer Vision techniques by Johannes Kasselman Rabie Thesis presented in partial fulfilment of the requirements for the Degree of MASTER OF ENGINEERING (EXTRACTIVE METALLURGICAL ENGINEERING) in the Faculty of Engineering at Stellenbosch University Supervisor Dr Lidia Auret March 2018 Stellenbosch University https://scholar.sun.ac.za DECLARATION By submitting this thesis electronically, I declare that the entirety of the work contained therein is my own, original work, that I am the sole author thereof (save to the extent explicitly otherwise stated), that reproduction and publication thereof by Stellenbosch University will not infringe any third party rights and that I have not previously in its entirety or in part submitted it for obtaining any qualification. Date: March 2018 Copyright © 2018 Stellenbosch University All rights reserved i Stellenbosch University https://scholar.sun.ac.za ABSTRACT Pellet-size estimation of a ferrochrome pelletizer circuit using Computer Vision techniques Rabie J.K., Auret L. Department of Process Engineering, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa. Thesis: M.Eng (Extractive Metallurgical Engineering) March 2018 Agglomerate pellet size plays an integral part in the safe and stable operation of a submerged arc furnace (SAF), and the efficiencies and yields achieved within the ferrochrome refining processes. For effective process control that ensures constant and optimal pellet size production, the continuous monitoring of pellet size distribution produced by the agglomeration circuit becomes imperative. Traditional size estimation methods tend to be labour intensive and time consuming, and cannot provide feedback in real time. The need therefore exists for automated, real time, and non-intrusive industrial size estimation systems. Despite major advances in the field and proven advantages with regards to object identification and analysis, image analysis-based size estimation systems have not experienced widespread implementation in the mineral processing environment. Cost and problem specific implications have been cited as the main factors inhibiting implementation. In an attempt to prove its viability, this study was aimed at developing a Digital Image Processing (DIP) and Digital Image Analysis (DIA) based particle size estimation algorithm that is suitable for implementation as part of a conceptual particle size distribution estimation sensor at a FeCr pelletizing plant, specifically at Glencore Plc‘s Bokamoso Pelletizing Plant. Additionally it had to explore the viability of the implementation of the sensor as part of a continuous monitoring and control system for a FeCr pelletizing process. This would be done through the development of a conceptual control framework for a FeCr pelletizing circuit. The algorithm was tested and validated on both simulated pelletizer circuit footage and actual process footage, with the former being made possible by the construction of a lab- scale set-up of a section of a FeCr pelletizing circuit. Estimated pellet size distributions were compared to sieve size distributions and a pixel to mm ratio. Results of analyses of both types of footage showed that the algorithm was capable of accurately estimating particle size distribution of moving FeCr pellets. In terms of industry application, the results point to a solution that analyses sintered pellet on conveyor footage as opposed to pellets on roller footage. Furthermore, the conceptual control framework suggests that the output of the algorithm can be successfully utilised in a control system that aims to control the size of FeCr pellets produced by a FeCr pelletizing circuit. ii Stellenbosch University https://scholar.sun.ac.za The use of problem specific filters aided in the accuracy of the algorithm in terms of identifying and delineating objects of interest, and thus ensured its applicability. It is however recommended that future studies investigate methods in which size estimation error associated with irregularly shaped particles is mitigated. Furthermore, it is also recommended to investigate and apply methods that would enable the algorithm to correctly interpret surface pellet data, in terms of pellet on conveyor footage, and subsequently correctly infer information regarding the entire population. iii Stellenbosch University https://scholar.sun.ac.za UITTREKSEL Korrelgrootteberaming van ‘n ferrochroom verkorrelingaanleg deur middel van Rekenaarvisie tegnieke (“Pellet-size estimation of a ferrochrome pelletizer circuit using Computer Vision techniques”) Rabie J.K., Auret L. Departement Prosesingenieurswese, Universiteit Stellenbosch, Privaatsak X1, Matieland 7602, Suid-Afrika. Tesis: M.Ing (Ekstraktiewe Metallurgiese Ingenieurswese) Maart 2018 Agglomeraat korrelgrootte speel ‗n integrale rol in die veilige en stabiele werking van ‗n boogoond, asook in die doeltreffendheid en opbrengste wat behaal word in die ferrochroom ontginningsproses. Vir doeltreffende prosesbeheer wat die produksie van konstante en optimale korrelgrootte verseker, word die deurlopende monitering van die korrelgrootteverspreiding, wat deur die verkorrelingaanleg geproduseer word, genoodsaak. Tradisionele grootteberamingstegnieke is tipies baie arbeidsintensief en tydrowend, en kan nie in reële-tyd terugvoer verskaf nie. Gevolglik bestaan daar ‗n behoefte vir geoutomatiseerde, reële-tyd en nie-indringende, industriële grootteberamingsisteme. Ten spyte van die groot vordering in die veld en die beproefde voordele met betrekking tot objekidentifikasie en –analise, het grootteberamingsisteme wat gebaseer is op beeld-analise nog nie grootskaalse implementering in die mineraalprosesseringindustrie ondergaan nie. Koste en probleem-spesifieke implikasies is geoormerk as die hoof faktore wat hierdie implimentering onderdruk. In ‗n poging om die lewensvatbaarheid van so ‗n proses te bewys, het hierdie studie gepoog om ‗n partikelgrootteberamingalgoritme te onwikkel wat op digitale beeldprosessering en – analise gebaseer is. Hierdie algoritme moes verder ook geskik wees om geïmplimenteer te word as deel van ‗n konseptuele partikelgrootteverspreidingberamingsensor by ‗n FeCr verkorrelingaanleg, spesifiek by Glencore Plc se Bokamoso verkorrelingaanleg. Daarbenewens moes die studie ook ondersoek instel rakende die lewensvatbaarheid om hierdie sensor te implementeer as deel van ‗n stelsel wat deurlopende monitering en beheer toepas op ‗n FeCr verkorrelingaanleg. Hierdie lewensvatbaarheid sou bewys word deur die ontwikkeling van ‗n konseptuele beheerraamwerk vir ‗n FeCr verkorrelingaanleg. Die algoritme was getoets en geldig verklaar op beelde van beide ‗n nagebootsde verkorrelingproses en ‗n werklike verkorrelingproses. Eersgenoemde is moontlik gemaak deur die bou van ‗n laboratorium-grootte nabootsing van ‗n gedeelte van ‗n FeCr verkorrelingaanleg. Beraamde korrelgrootteverspreidings is toe met sif-grootte verspreidings vergelyk, asook met ‗n ―pixel‖ tot mm verhouding. iv Stellenbosch University https://scholar.sun.ac.za Die resultate van die ontledings van beide tipes beelde het bevestig dat die algoritme in staat is om korrelgrootteverpreiding van bewegende FeCr korrels akkuraat te beraam. Met betrekking tot die idustriële toepassing van die algoritme, dui die resultate op ‗n oplossing wat beelde analiseer van gebakte korrels wat op vervoerbande vervoer word, eerder as beelde van korrels wat oor rollers beweeg. Verder dui die konseptuele beheerraamwerk daarop dat die afvoer van die algoritme suksesvol gebruik sal kan word in ‗n beheerstelsel wat daarop gemik is om die grootte van FeCr korrels te beheer wat deur ‗n verkorrelingaanleg geproduseer word. Deur gebruik te maak van probleemspesifieke filters kon die akkuraatheid van die algoritme, in terme van die identifisering en afsondering van partikels, verhoog word, en gevolglik die toepaslikheid van die algoritme verseker word. Dit is egter aanbevole dat toekomstige studies ondersoek moet instel rakende metodes wat die fout kan verminder of uitskakel wat met grootteberaming van onreëlmatig-gevormde partikels gepaard gaan. Dit word verder ook aanbeveel dat ondersoek ingestel moet word rakende metodes wat die algoritme in staat sal stel om data rakende die korrels op die oppervlak van ‗n vervoerband korrek te interpreteer, en gevolglik die korrekte aannames te maak oor die hele populasie. v Stellenbosch University https://scholar.sun.ac.za ACKNOWLEDGEMENTS I would like to express my sincere gratitude, first and foremost, to my Lord, who has granted me with the abilities I possess in life. Secondly, my deepest gratitude is extended to my supervisor, Dr L. Auret, for her unwavering support, guidance, and belief in my abilities, and for the friendship that has developed over the duration of the study. A big thank you is extended to Glencore, who have made this study possible. And a special thank you is extended to the personnel at Glencore‘s Wonderkop Smelter, from the admin to the technical, and including, but not limited to, Mr H. Potgieter, Mr J. Botha and Mr A Gloy. Thank you for never hesitating to accommodate me and go the extra mile in assisting with whatever was needed in the execution of this study. I also thank the workshop personnel of the Department of Process Engineering at Stellenbosch University for the great contribution with regards to the lab-scale roller feeder built for the purposes of this study. Thank you to Mr M. Kotzé for his dogged motivation throughout the course
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